A technique of generating electric power using a piezoelectric effect of a piezoelectric body has been developed. For example, a power generating device disclosed in Japanese Patent Laying-Open No. 2012-254005 (Patent Document 1) includes: a piezoelectric member formed of a piezoelectric material; a pair of electrodes provided on the piezoelectric member; a deformation member that repeatedly deforms the piezoelectric member; an inductor provided between the pair of electrodes, the inductor and a capacitance component of the piezoelectric member constituting a resonance circuit; a switch connected to the inductor in series; a voltage detecting unit that detects a voltage of the piezoelectric member; and a control unit that determines whether a first voltage detected by the voltage detecting unit is a maximal value or a minimal value.
In addition to this, power generating devices employing such a piezoelectric effect are also disclosed in, for example, Japanese Patent Laying-Open No. 2012-175712 (Patent Document 2), Japanese Patent Laying-Open No. 2012-105518 (Patent Document 3), Japanese Patent Laying-Open No. 2012-110143 (Patent Document 4), US Patent Application Publication No. 2010/0079034 (Patent Document 5), Japanese Patent Laying-Open No. 2012-65533 (Patent Document 6), and Yogesh K. Ramadass et al., “An Efficient Piezoelectric Energy Harvesting Interface Circuit Using a Bias-Flip Rectifier and Shared Inductor”, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL 45, No. 1, JANUARY 2010 (Non-Patent Document 1).
In general, when charges are generated in a piezoelectric body, mechanical force is generated due to an inverse piezoelectric effect. Depending on a state of distribution of the charges generated in the piezoelectric body, this force can act in a direction that hinders vibration of the piezoelectric body. Moreover, the magnitude of this force is proportional to an amount of the charges generated in the piezoelectric body. As the amplitude of vibration of the piezoelectric body is increased, the amount of the charges generated in the piezoelectric body is increased, but the force generated due to the inverse piezoelectric effect is also increased. Disadvantageously, this leads to a decreased amount of electric power generated by the power generating device.